Clinton ran the so-called 3 am ad questioning whether Obama could handle a national security crisis in the middle of the night. McCain ran his own ad casting doubt on Obama's readiness. He ridiculed the Democrat for playing basketball on his overseas trip and accused him of skipping a visit to wounded soldiers because the Pentagon wouldn't let him bring TV cameras.

She embraced the controversial gas-tax holiday in arguing that she better understood the economic struggles of blue collar voters. McCain went further, pressing expanded offshore drilling while deriding Obama as Dr. No on energy.

She exploited his vulnerabilities with older voters and whites in the Rust Belt. McCain's doing the same thing, turning Ohio, Michigan and Pennsylvania into general election battlegrounds.

The Clinton campaign complained of media bias; Team McCain has claimed the media is "in love" with Obama.

So far, Obama leads – but narrowly, as he did in his victory over Clinton in Democratic primaries.

But elements of Obama-McCain fight may resonate differently than in Obama-Clinton – and the winning candidate may be the one who better adapts to those differences.

Press-bashing, a unifying theme for Republicans, could help McCain more than Clinton.

So could racial polarization, since general election swing voters are more conservative than those who vote in Democratic primaries.

But Obama has one big advantage this fall that wasn’t available against Mrs. Clinton, whose policy positions closely resembled his own.

On touchstone issues like taxes, health care and the Iraq War, McCain remains aligned with President Bush, whose approval rating continues to hover around 30%.

That’s why Obama released a new ad today attacking McCain on energy – and linking him to Bush.